Aid in the diagnosis of vonWillebrand Disease and of diseases with changes in the Ristocetin Cofactor activity, such as vascular endothelial lesions, inflammations, and preoperative screening of bleeding tendency.

Ristocetin cofactor (vW factor; VIII:vW; vonWillebrand factor) is the property of the Factor VIII protein that is responsible for the agglutination of platelets in the presence of ristocetin. Decreased quantities or abnormalities of the vonWillebrand factor are associated with vonWillebrand syndrome, thus making quantitation of the factor most valuable in the diagnosis and evaluation of this coagulopathy.Levels of vonWillebrand factor are determined by the ability of a test plasma and ristocetin to induce agglutination of a standardized platelet suspension.